This application is the national phase under 35 U.S.C. xc2xa7 371 of PCT International Application No. PCT/JP99/04682 which has an International filing date of Aug. 30, 1999, which designated the United States of America.
1. Technical Field
The present invention relates to an optical switching system for carrying out path switching on a network that interconnects a plurality of nodes through a working path and a preparatory path using optical signals.
2. Background of the Invention
FIG. 1 is a block diagram showing a partially redrawn conventionally studied optical switching system as disclosed under the title of xe2x80x9cWDM four fiber ring experimentxe2x80x9d, B-10-230, page 739, Proceedings of the 1997 IEICE (the Institute of Electronics, Information and Communication Engineers of Japan) General Conference; and FIG. 2 is a partially redrawn operational diagram illustrating a path switching operation in case of a fault described in this paper.
In FIG. 1, a reference numeral 101 designates an acoustooptic filter for isolating any desired wavelength component; 102 designates a 4xc3x974 optical space switch for connecting four optical inputs to four output ports in any desired pattern; 103 designates a recombining element for recombining optical signals; 104 designates an optical amplifier for collectively amplifying wavelength multiplexed optical signals; 105 designates a terminal unit for transmitting and receiving optical signals; 106 designates an east side (denoted as xe2x80x9cEast sidexe2x80x9d from now on) working input/output port (denoted as xe2x80x9cWRK in/out portxe2x80x9d from now on) for interconnecting a working path between nodes; 107 designates a west side (denoted as xe2x80x9cWest sidexe2x80x9d from now on) WRK in/out port for interconnecting the working path between nodes; 108 designates an East side preparatory input/output port (denoted as xe2x80x9cPRT in/out portxe2x80x9d from now on) for interconnecting a preparatory path between the nodes; and 109 designates a west side PRT in/out port for interconnecting the preparatory path between the nodes.
In FIG. 2, reference numerals 111-114 each designate a node corresponding to the optical switching system as shown in FIG. 1; 115 designates an inside transmission path for transmitting optical signals in both directions used as the working path for interconnecting the nodes. The reference numeral 116 designates an outside path for transmitting optical signals in both directions used as the preparatory path for interconnecting the nodes. Reference numerals 117 each designate a 4xc3x974 optical space switch in the node; 118 each designate a working terminal unit connected to the node; and 119 each designate a preparatory terminal unit.
Next, the operation will be described.
In FIG. 2, the transmission paths 115 and 116 that interconnect the nodes 111-114 are wavelength multiplexed, and are connected to the WRK in/out ports 106 and 107 and PRT in/out ports 108 and 109 of the optical switching system of FIG. 1. Each acoustooptic filter 101, receiving a drive signal, isolates a particular wavelength signal to be connected to the optical space switch 102, and passes the remaining wavelength signals without change. Without the drive signal, all the wavelength optical signals pass through the acoustooptic filters 101. Thus, each acoustooptic filter 101 is used as a switch for switching whether to remove (denoted as xe2x80x9cDropxe2x80x9d from now on) the wavelength from the transmission path or not by the drive signal.
The isolated signals output from the acoustooptic filters 101 are connected to appropriate terminal units 105 via the optical space switches 102 to be received. The individual nodes are each connected to four terminal units 105, so that they are connected to East side and West side WRK in/out ports and PRT in/out ports.
The optical signals input to the optical switching system through the terminal units 105 are distributed to the appropriate recombining elements 103 at the output ports by the optical space switches 102, recombined with the optical signals of other wavelengths passing through the acoustooptic filters 101, and transmitted to adjacent nodes through the output ports as wavelength multiplex signals.
The optical space switches 102 switch, if some fault takes place on the transmission path, the communications on the working system to the recombining elements 103 on the same or reverse direction preparatory path in accordance with the fault pattern, thereby saving the communications on the working system at the cost of the communications on the preparatory system.
Thus, the network is constructed by providing the nodes of the transmission paths with the optical switching system with the foregoing functions and by connecting the transmission paths in a ring-like pattern.
Next, an example of the switching operation in case of a network fault will be described with reference to FIG. 2.
In a normal operation mode in which no fault takes place, communications can be carried out using the working path and preparatory path as shown in FIG. 2(1). For example, the working terminal units 118 connected to the node 111 and to the node 113 are bidirectionally interconnected through the working path 115, and the terminal units 119 connected to the node 113 and to the node 114 are bidirectionally interconnected through the preparatory paths 116.
If a fault takes place on the working path 115 interconnecting the nodes 111 and 113, and the preparatory path passing through the same route is in a faultless state, the optical space. switches 117 of the nodes 111 and 113 that carry out transmission and reception are switched to the preparatory paths of the same direction as shown in FIG. 2(2), so that the communication path used by the working terminal unit 118 is switched to the preparatory path passing through the same route, thereby detouring the signal flowing through the transmission path 115 to the transmission path 116, and preventing the transmission path from being disconnected.
If a fault takes place simultaneously on both transmission paths 115 and 116 interconnecting the nodes, the optical space switches 117 of the nodes 111 and 113 switch the input/output ports for transmission and reception to the opposite preparatory path side as shown in FIG. 2(3), thereby detouring the signals to the transmission path 116 passing through the network in the opposite direction, and preventing the working path from being disconnected. In this case, the communications carried out between the nodes 113 and 114 using the transmission path 116 in the faultless state are disconnected to prevent the disconnection of the working transmission path.
FIG. 3 is a block diagram showing another partially redrawn conventionally studied optical switching system as disclosed under the title of xe2x80x9cNode configuration on OADM ring systemxe2x80x9d, B-10-85, page 384, Proceedings of the 1997 Society Conference of the Institute of Electronics, Information and Communication Engineers of Japan.
In FIG. 3, reference numerals 121 each designate an optical switching system that receives currently working signals, and switches, in case of a transmission path fault, an optical signal path to an unimpaired transmission path; the reference numeral 122 designates a backup optical switching system used in place of one of the optical switching systems 121 when it is faulty; xcex(1)xe2x88x92xcex(n+1) each designate an optical signal with a different wavelength; reference numerals 127-128 each designate a terminal unit connected to the optical switching system 121 and 122 for transmitting and receiving the optical signals xcex(1)xe2x88x92xcex(n+1); 123 and 124 each designate a wavelength multiplexer for wavelength multiplexing the optical signals xcex(1)xe2x88x92xcex(n+1) with different wavelengths transmitted from the terminal units 127-128, and for sending them out to transmitting paths; 125 and 126 each designate a wavelength demultiplexer for demultiplexing the wavelength multiplex signals fed from receiving paths for respective wavelengths, and for inputting them to the optical switching systems corresponding to the optical signals xcex(1)xe2x88x92xcex(n+1) with different wavelengths; 131 designates intra-office interfaces for inputting signals to be transmitted to the transmission paths; 132 designates intra-office interfaces for outputting signals received from the transmission paths; and 129 and 130 each designate an (n+1):n electric switch for recovering, when a fault takes place in a certain unit associated with a particular wavelength among the terminal units 127-128 or optical switching systems 121 provided for each of the n wavelengths, the fault by switching the transmitted and received signals associated with the unit corresponding to that faulty wavelength to the backup unit corresponding to the (n+1) th wavelength.
The reference numeral 24 designates a transmitting section installed in each optical switching system 121; 23 designates a receiving section installed in each optical switching system 121; 11 designates a working transmitted optical signal splitter provided for each transmitting section 24; and 22 designates a working received optical signal selector provided for each receiving section 23.
Next, the operation will be described.
The conventional example assumes to be applied to a ring network employing the bidirectional transmission paths that enable individual communications for respective wavelengths based on the wavelength multiplexing technique. Communication paths for optical signals of respective wavelengths comprise terminal units 127-128 and optical switching systems 121 and 122, and are connected to the transmission paths through the wavelength multiplexers 123 and 124 and the wavelength demultiplexers 125 and 126. The n intra-office interfaces 131 or 132 for outputting or inputting the optical signals to be transmitted or received correspond to n+1 wavelengths prepared in advance, and the n working channels have one preparatory channel, constituting a 1:n configuration.
If a fault takes place in a terminal unit or in an optical switching system associated with a particular wavelength, the intra-office interface associated with the fault is connected to the preparatory channel through the (n+1):n electric switch 129 or 130, thereby recovering the fault of the system.
If a fault takes place in a transmission path, the fault is recovered by the switching operation of the optical switching systems 121 and 122. The transmitting section of each of the optical switching systems 121 and 122 associated with respective wavelengths divides the transmitted signal into two with the working transmitted optical signal splitter 11, and sends them to the two transmitting paths. On the other hand, in each receiving section, the working received optical signal selector 22 selects one of the optical signals fed from the two receiving paths. If a fault takes place on one of the two receiving paths, the working received optical signal selector 22 selects the remaining faultless receiving path to recover the fault of the transmission path.
The conventional optical switching systems have the foregoing configurations. The first conventional example as shown in FIGS. 1 and 2 disclosed in the B-10-230 paper employs, when the network is normal, both the working path and preparatory path separately for different communications, whereas in case of a fault it detours the currently working signals to the preparatory path using the 4xc3x974 optical space switches 102 or 117 for the path switching. This presents a problem in that the 4xc3x974 optical space switches 102 or 117 utilizing waveguides have not yet reached a level required for practical applications in the characteristics such as an extinction ratio or loss, or reliability and power consumption.
On the other hand, the 4xc3x974 optical space switches 102 or 117 utilizing mechanical optical space switches can meet the foregoing characteristics with the reliability of practical level, and the mechanical switches with a latch function have an advantage of being able to eliminate the power required for holding the present state. These switches, however, have a problem of increasing packaging dimensions because the function of a unit switch is limited to 1xc3x972 or 2xc3x972, which means that 16 unit switches are required to implement the 4xc3x974 optical space switch 102 or 117 by combining the 2xc3x972 unit switches.
Furthermore, when a 4xc3x974 optical space switch 102 or 117 in a certain node has to be replaced because of a fault, the conventional example has a problem of interrupting during the recovery job all the communications passing through the terminal units 105, 118 or 119 connected to the node because all the transmitted or received signals connected to the terminal units 105, 118 or 119 are connected to a single optical space switch 102 or 117.
The conventional example as shown in FIG. 3 disclosed in the, B-10-85 paper divides the output signals from the optical switching systems 121 and 122 to the two transmitting paths so that the two paths transmit the same signals. This presents a problem in that the working efficiency of the transmission paths is limited to xc2xd because the network always transmits the same signals through the two paths.
The present invention is implemented to solve the foregoing problems. Therefore, an object of the present invention is to provide an optical switching system with high transmission path working efficiency without interrupting all the communications during the recovery job such as component replacement in case of a fault of an optical space switch by decreasing the number of the optical space switches, thereby reducing the packaging size with maintaining the characteristics and reliability of the optical space switches.
The optical switching system according to the present invention comprises a receiving section including a receiving optical switch for receiving an optical signal input to a working input port and an optical signal input to a preparatory input port, for outputting as two output signals the two input signals by spatially switching their paths or by passing them through, and for connecting a first output of the two output signals to a working drop port, and a preparatory receiving optical gate for turning on or off a second output signal from the receiving optical switch to be supplied to a preparatory drop port.
According to the present invention, a transmitting section comprises a working transmitted optical signal splitter and a preparatory transmitted optical signal selector, and the receiving section comprises the receiving optical switch and the preparatory receiving optical gate. If a fault takes place in the working path while the preparatory path conveys a signal such as an extra traffic signal different from the signal on the working signal in a faultless state, the preparatory receiving optical gate breaks the optical signal to be supplied to the preparatory drop port, thereby preventing the working signal from being erroneously connected to the preparatory drop port when the switching operation is carried out in the fault. This offers an advantage of being able to make full use of the total transmission capacity of both the working path and preparatory path in the faultless state, which increases the working efficiency of the transmission path.
Furthermore, because the receiving section can be configured using one 2xc3x972 optical space switch and one optical gate, the packaging dimension can be reduced. Since the number of switches is small, even mechanical optical switches, which have effective characteristics and. functions, are applicable with practical packaging size.
Moreover, the transmitting section can be physically divided into optical components through which the working signal passes, and into optical components through which the preparatory signal passes, which presents an advantage of being able to improve the reliability in the system maintenance.
In addition, the transmitting section can be configured with one coupler and one 1xc3x972 optical space switch, which offers an advantage of being able to reduce the packaging dimension. Since the number of switches is small, even mechanical optical switches, which have effective characteristics and functions, are applicable with practical packaging size.
The optical switching system according to the present invention comprises a receiving section including a preparatory receiving optical switch for receiving an optical signal input to a preparatory input port, for spatially switching a path of the input optical signal to two outputs, and for connecting a first output of the two outputs to a preparatory drop port, and a working received optical signal selector for receiving a second output of the preparatory receiving optical switch and an optical signal input to a working input port, and for selecting one of the two inputs to be supplied to a working drop port.
According to the present invention, the receiving section is configured such that it comprises the preparatory receiving optical switch and the working received optical signal selector. If a fault takes place in the working receiving path, the working received optical signal selector carries out switching to select the optical signal from the preparatory receiving path, with breaking the optical signal from the working receiving path. At the same time, the preparatory receiving optical switch stops supplying the optical signal to the preparatory drop port in the fault switching. This enables the communication to make full use of the total transmission capacity of both the working path and the preparatory path in the faultless state, improving the transmission path working efficiency.
Furthermore, in a faultless state, the optical components through which the working signal passes can be physically divided from the optical components through which the preparatory signal passes. This makes it possible for the boards mounting the optical switches to be packaged separately for the working path and preparatory path. Thus, even if a fault takes place in an optical switch element, the recovery job can be achieved in some cases by only replacing the board mounting the working path without removing the connection of the preparatory path, for example. This will improve the reliability of the system.
Moreover, the switch configuration of the receiving section can be implemented using two 1xc3x972 optical space switches, which offers an advantage of being able to reduce the packaging size. Since the number of the switches is small, even mechanical optical switches, which have effective characteristics and functions, are applicable with practical packaging size.
Furthermore, because the transmitting section can be physically divided into optical components through which the working signal passes, and into optical components through which the preparatory signal passes, the reliability in the system maintenance can be improved.
In addition, the switch configuration of the transmitting section can be implemented using one coupler and one 1xc3x972 optical space switch, which offers an advantage of being able to reduce the packaging dimension. Since the number of switches is small, even mechanical optical switches, which have effective characteristics and functions, are applicable with practical packaging size.
The optical switching system according to the present invention comprises a receiving section including a preparatory receiving optical splitter for dividing into two an optical signal input to a preparatory input, and for outputting them, a working received optical signal selector for receiving a first output of the two outputs of the preparatory receiving optical splitter and an optical signal input to a working input port, and for selecting one of the two inputs to be supplied to a working drop port, and a preparatory receiving optical gate for turning on or off a second output of the preparatory receiving optical splitter to be supplied to a preparatory drop port.
According to the present invention, the receiving section is configured such that it comprises the preparatory receiving optical splitter, the working received optical signal selector and the preparatory receiving optical gate. If a fault takes place in the working receiving path, the preparatory receiving optical gate breaks the optical signal sent from the working receiving path to prevent the optical signal from being supplied to the preparatory drop port. This enables the communication to make full use of the total transmission capacity of both the working path and preparatory path in the faultless state, improving the transmission path working efficiency.
Furthermore, in the faultless state, the optical components through which the working signal passes can be physically divided from the optical components through which the preparatory signal passes. This makes it possible, even if a fault takes place in an optical switch element or the like, to carry out a recovery job by only replacing the board mounting the working path without removing the connection of the preparatory path, for example. This will improve the reliability of the system.
Moreover, the switch configuration of the receiving section can be implemented using one coupler, one 1xc3x972 optical space switches and one optical gate, which offers an advantage of being able to reduce the packaging size. Since the number of the switches is small, even mechanical optical switches, which have effective characteristics and functions, are applicable with practical packaging size.
Furthermore, because the transmitting section can be physically divided into optical components through which the working signal passes, and into optical components through which the preparatory signal passes, the reliability in the system maintenance can be improved.
In addition, the switch configuration of the transmitting section can be implemented using one coupler and one 1xc3x972 optical space switch, which offers an advantage of being able to reduce the packaging dimension. Since the number of switches is small, even mechanical optical switches, which have effective characteristics and functions, are applicable with practical packaging size.
The optical switching system according to the present invention comprises a working add/drop switch with two inputs and two outputs for passing through or for switching optical signals input to a working input port and to a working add port, and for supplying the optical signals to a transmitting section and to a receiving section of the optical switching system; and a preparatory add/drop switch with two inputs and two outputs for passing through or switching optical signals input to a preparatory input port and to a preparatory add port, and for supplying the optical signals to the transmitting section and to the receiving section of the optical switching system.
According to the present invention, the optical switching system is configured such that it comprises the working add/drop switch and the preparatory add/drop switch, and these add/drop switches can readily implement the add/drop switching with two 2xc3x972 optical switches. This offers an advantage of being able to construct the optical switching system applicable to a ring network with a small number of unit optical switches, thereby shrinking the packaging dimension.
In addition, because it is possible to make full use of the total transmission capacity of both the working path and preparatory path in the faultless state, the transmission path working efficiency can be improved.
Moreover, applying the optical switching systems can bidirectionally interconnect any desired nodes in a ring network including a plurality of nodes interconnected. This offers an advantage of being able to improve the flexibility of the network.
The optical switching system according to the present invention comprises span switching means provided for each one of sets for switching between a working path and a preparatory path in the same section by switching or by passing through input and output optical signals from and to working input/output ports and from and to preparatory input/output ports; first ring switching means for supplying the span switching means of a first one of the sets with input and output signals associated with a preparatory add port of the first one of the sets, with a working add port of the first one of the sets, with a working drop port of the first one of the sets, and with a preparatory drop port of the first one of the sets by switching or passing through them; and second ring switching means for supplying the span switching means of a second one of the sets with input and output signals associated with a preparatory add port of the second one of the sets, with a working add port of the second one of the sets, with a working drop port of the second one of the sets, and with a preparatory drop port of the second one of the sets by switching or passing through them.
According to the present invention, the optical switching system is configured such that it comprises for each of the two sets the span switching means and the first and second ring switching means. The ring switching means can configure anther preparatory path in a reverse direction even if both the working path and preparatory path fall into a fault at the same time in a particular section of the ring network. The span switching means can detour the signals to the preparatory path in the same section when only the working path falls into a fault and the preparatory path is normal in the section. Providing the two switching modes can improve the reliability of the network.
Furthermore, because both the ring switching means and span switching means are composed of the optical space switches, the number of the optical switches required is small, offering an advantage of being able to reduce the packaging size.
Moreover, because the total transmission capacity of both the working path and preparatory path can be utilized in the faultless state, the working efficiency of the transmission paths can be improved.